1. Field of the Invention
The present invention relates to a semiconductor device having a circuit comprised of thin film transistor (hereinafter, TFT) and a manufacturing method thereof. For instance, the present invention relates to a light emitting device using a light emitting element which has a film containing an organic compound (hereinafter, organic compound layer) between a pair of electrodes and which can give fluorescence or luminescence by receiving an electric field, and a manufacturing method thereof. The light emitting device referred to in the present specification is an image display device, a light emitting device or a light source (including lighting installation). Additionally, the following are included in examples of the light emitting device: a module wherein a connector, for example, a flexible printed circuit (FPC) or a tape automated bonding (TAB) tape, or a tape carrier package (TCP) is set up onto a light emitting element; a module wherein a printed wiring board is set to the tip of a TAB tape or a TCP; and a module wherein integrated circuits (IC) are directly mounted on a light emitting element in a chip on glass (COG) manner.
In addition, the semiconductor device in this specification is the device in general which can function by utilizing the semiconductor characteristics. An electro-optic device, a light emitting device, a semiconductor circuit and an electronic device are all semiconductor devices.
2. Related Art
A light emitting element using an organic compound as a luminous body, characterized by its thin thickness, light weight, high-speed response, low-voltage DC drive, and so on, has been expected its application to a next-generation flat panel display. Especially a display device, in which light emitting elements are arranged in a matrix configuration, is considered that it has an advantage over the conventional liquid crystal display device in terms of its wide angle and superior visibility.
A light emitting mechanism of a light emitting element may be as follows. That is, when a voltage is applied on the organic compound layer sandwiched between a pair of the electrodes, an electron injected from the cathode and an electron hole injected from the anode are brought into recombination with each other at the luminescence center of the organic compound layer to form a molecular excitation. Subsequently, light emission is occurred by discharging energy when the molecular excitation returns to a ground state. There are two types of the excitation state, a singlet exciton and a triplet exciton. The light emission may achieved in either state.
The light emitting device constructed of a plurality of light emitting elements arranged in a matrix configuration may be operated by a passive matrix drive (passive matrix type) and an active matrix drive (active matrix type). However, when the pixel density increases, it may be preferable to use the active matrix type in which a switch is provided for every pixel (or every dot) since it can be driven at a low voltage.
Furthermore, low-molecular type material and high-molecular type (polymer) material have been studied for an organic compound to be provided as an organic compound layer (i.e., a light emitting layer in the strict sense), which may be a center of a light emitting element. Among them, the attention has been focused on the high-molecular type material because of its high heat resistance and convenience in handling compared with the low-molecular type material.
For forming a film from an organic compound, vapor deposition, spin-coating, and ink-jetting have been known. Among them, for realizing a full-color image formation using a polymer material, the spin-coating and the ink-jetting have been particularly known.
The disadvantage of a light emitting element having an organic compound is easily deteriorated by various factors, so that the greatest object thereof is to increase its reliability (make longer its life span).
A light emitting element having an organic compound is deteriorated mainly by oxygen and moisture. As a defective state due to this, the partial deterioration of luminance and nonluminous region are occurred.
The expansion of nonluminous region may proceed merely with time or with time during which light emitting element is driven. Particularly, in the case nonluminous region is occurred soon after manufacturing a light emitting material having an organic compound, the expansion of nonluminous region is often proceeded with time, and is sometimes end up with whole nonluminous region.
In addition, the nonluminous region tends to generate from a marginal portion of luminous region, and expands with time as if contracting the luminous region. Therefore, this defective mode is called shrink.
These defects cause a certain light emitting element to be a nonluminous element at high speed, particularly, with respect to an active matrix type light emitting device, because shrink heavily damages such a small light emitting region in the active light emitting device. Further, in the case the area of luminous region is small, the proportion of nonluminous region becomes bigger, according to the reduction of luminous region. Therefore, when manufacturing a display device using a light emitting element, it is difficult to obtain a display device which has a high-definition (basically a pitch of a pixel area is small) and higher reliability.
Non luminous region such as a black spot may be generated just after manufacturing a light emitting element having an organic compound, This defective mode is referred to as dark spot. And this dark spot may be enlarged with time.